The present invention is directed to a method of making an improved ultra soft, multi-ply product. More particularly, the present invention is directed to a method of making an ultra soft, multi-ply tissue from non-premium, high coarseness, or secondary fiber furnish. Still further, the present invention is directed to improving the CD tensile energy absorption of a multi-ply product. Finally, the present invention is directed to an ultra soft bathroom tissue produced according to the described method.
In the area of bathroom tissue, softness, absorbency and strength are key attributes considered by consumers. It is highly desirable that the tissue product have a consumer perceived feel of softness. This softness plays a key role in consumer preference. Softness relates both to the product bulk and surface characteristics. In addition to softness, the consumer desires a product that is both strong and absorbent to minimize the amount of the product which must be used to do an effective job.
The method of the present invention uses wet press technology to prepare a strong, ultra soft tissue having a high basis weight. The tissue produced by the method of the present invention exhibits good strength and absorbency while remaining extremely soft. The method according to the present invention results in a product having improved CD tensile energy absorption, which bears substantial correspondence to consumer perceptions of strength. Properties such as those exhibited by the tissue of the present invention have not heretofore been seen in wet-press tissue products.
In a conventional wet press (CWP) process and apparatus (10), as exemplified in FIG. 1, a furnish is fed from a silo (50) through conduits (40, 41) to headbox chambers (20, 20xe2x80x2). A web (W) is formed on a conventional wire former (12), supported by rolls (18, 19), from a liquid slurry of pulp, water and other chemicals. Materials removed from the web of fabric in the forming zone when pressed against a forming roll (15) are returned to a silo (50), from a saveall (22) through a conduit (24). The web is then transferred to a moving felt or fabric (14), supported by a roll (11) for drying and pressing. Materials removed from the web during drying and pressing or from a Uhle box (29) are collected in a saveall (44) and fed to a white water conduit (45). The web is then pressed by a suction press roll (16) against the surface of a rotating Yankee dryer cylinder (26) which is heated to cause the paper to substantially dry on the cylinder surface. The moisture within the web as it is laid on the Yankee surface causes the web to transfer to the surface. Liquid adhesive may be applied to the surface of the dryer to provide substantial adherence of the web to the creping surface. The web is then creped from the surface with a creping blade (27). The creped web is then usually passed between calender rollers (30) and rolled up on a roll (28) prior to further converting operations, for example, embossing. The action of the creping blade on the paper is known to cause a portion of the interfiber bonds within the paper to be broken up by the mechanical smashing action of the blade against the web as it is being driven into the blade. However, fairly strong interfiber bonds are formed between the wood pulp fibers during the drying of the moisture from the web. The strength of these bonds in prior art tissues is such that, even after creping, the web retains a perceived feeling of hardness, a fairly high density, and low-bulk and water absorbency.
To reduce the strength of the interfiber bonds that inevitably result when wet pressing and drying a web from a slurry, various processes have been utilized. One such process is the passing of heated air through the wet fibrous web after it is formed on a wire and transferred to a permeable carrierxe2x80x94a so-called through-air-dried (TAD) processxe2x80x94so that the web is not compacted prior to being dried. The lack of compaction, such as would occur when the web is pressed while on a felt or fabric and against the drying cylinder when it is transferred thereto, reduces the opportunity for interfiber bonding to occur, and allows the finished product to have greater bulk than can be achieved in a wet press process. Because of the consumer perceived softness of these products, and their greater ability to absorb liquids than webs formed in wet press processes, the products formed by the newer processes enjoy an advantage in consumer acceptance.
Felted wet press processes are significantly more energy efficient than processes such as through-air-drying since they do not require heating and moving large quantities of air as required by the TAD process. In wet press operations, excess moisture is mechanically pressed from the web and the final drying of the web is obtained chiefly on the heated Yankee drying cylinder which is maintained at the proper drying temperature.
The present invention provides a method for making a tissue product that achieves high strength, bulk, absorbency, and softness above existing conventional wet-pressed tissue, approaching or achieving levels even beyond those found using through-air-drying. The process according to the present invention uses the cheaper more efficient wet press process and also uses less expensive, non-premium fibers.
Further advantages of the invention will be set forth in part in the description which follows. The advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing advantages and in accordance with the purpose of the invention as embodied and broadly described herein, there is disclosed:
A method of making an ultra-soft high basis weight multi-ply tissue including:
(a) providing a fibrous pulp furnish wherein the total furnish has a fiber coarseness of at least about 11 mg/100 meters;
(b) forming a first nascent web from the furnish;
(c) including in the first web at least about 1.0 lbs/ton of a cationic nitrogenous softener;
(d) dewatering the first web through wet pressing;
(e) adhering the first web to a Yankee dryer;
(f) creping the first web from the Yankee dryer at a reel crepe of at least about 20%;
(g) forming a second nascent web as recited in steps (a)-(f) above;
(h) combining the first web with the second web to form a multi-ply web;
(i) embossing the multi-ply web between mated emboss rolls, each of which contains both male and female elements;
(j) optionally calendering the embossed multi-ply web; and
wherein steps (a)-(j) are controlled to result in a multi-ply tissue product having an MD tensile strength of about 21 to about 50 g/3xe2x80x3 width per lb. of basis weight; a CD tensile strength of about 10 to about 23 g/3xe2x80x3 width per lb. of basis weight; a caliper of at least about 3 mils/8 plies/lb. basis weight; a GM MMD friction of less than about 0.21; and a tensile stiffness of less than about 1 (g/inch/% strain)/(lb/ream); and a CD tensile absorption energy according to the following relationship
xe2x80x83CD TEAxe2x89xa7CDT*0.00085xe2x88x920.105.
There is further disclosed an ultra soft, high absorbency product produced by the above-described method.
Finally there is disclosed:
An embossed multi-ply tissue product including at least two paper webs each having a fiber coarseness of at least about 11 mg/100 meters; an MD tensile strength of about 21 to about 50 g/3xe2x80x3 width per lb. of basis weight; a CD tensile strength of about 10 to about 23 g/3xe2x80x3 width per lb. of basis weight; a caliper of at least about 3 mils/8 plies/lb. basis weight; a GM MMD friction of less than about 0.21; a tensile stiffness of less than about 1 (g/inch/% strain)/(lb/Ream); and a CD tensile absorption energy according to the following relationship
CD TEAxe2x89xa7CDT*0.00085xe2x88x920.105.